Embedding information in an 802.11 signal field

ABSTRACT

Techniques and apparatus for embedding one or more bits of 802.11 Very High Throughput (VHT) information in existing IEEE 802.11 preamble fields are provided. As will be described herein, because different combinations of modulation techniques, coding schemes, and transmission lengths result in the same transmit time (e.g., in terms of symbol length), a clever choice of modulation, coding, and length may allow some extra information to be embedded in a legacy field for use by VHT stations. In this manner, the total VHT preamble transmission time may potentially be reduced, thereby increasing the efficiency of the physical layer (PHY). Moreover, the embedded bits may most likely be invisible to legacy stations, since the transmission time that such stations compute will be independent of these bits by design.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of U.S. Provisional Patent ApplicationSer. No. 61/089,192, entitled “EMBEDDING INFORMATION IN 802.11N SIGNALFIELD” filed Aug. 15, 2008, which is herein incorporated by reference inits entirety.

FIELD

Certain embodiments of the present disclosure generally relate towireless communication and, more specifically, to embedding informationin an existing IEEE 802.11n field.

BACKGROUND

In order to address the issue of increasing bandwidth requirementsdemanded for wireless communication systems, different schemes are beingdeveloped to allow multiple user terminals to communicate with a singlebase station by sharing the same channel (same time and frequencyresources) while achieving high data throughputs. Spatial DivisionMultiple Access (SDMA) represents one such approach that has recentlyemerged as a popular technique for the next generation communicationsystems. SDMA techniques may be adopted in several emerging wirelesscommunications standards such as IEEE 802.11 (IEEE is the acronym forthe Institute of Electrical and Electronic Engineers, 3 Park Avenue,17th floor, New York, N.Y.) and Long Term Evolution (LTE).

In SDMA systems, a base station may transmit or receive differentsignals to or from a plurality of mobile user terminals at the same timeand using the same frequency. In order to achieve reliable datacommunication, user terminals may need to be located in sufficientlydifferent directions. Independent signals may be simultaneouslytransmitted from each of multiple space-separated antennas at the basestation. Consequently, the combined transmissions may be directional,i.e., the signal that is dedicated for each user terminal may berelatively strong in the direction of that particular user terminal andsufficiently weak in directions of other user terminals. Similarly, thebase station may simultaneously receive on the same frequency thecombined signals from multiple user terminals through each of multipleantennas separated in space, and the combined received signals from themultiple antennas may be split into independent signals transmitted fromeach user terminal by applying the appropriate signal processingtechnique.

A multiple-input multiple-output (MIMO) wireless system employs a number(N_(T)) of transmit antennas and a number (N_(R)) of receive antennasfor data transmission. A MIMO channel formed by the N_(T) transmit andN_(R) receive antennas may be decomposed into N_(S) spatial channels,where, for all practical purposes, N_(S)≦min{N_(T),N_(R)}. The N_(S)spatial channels may be used to transmit N_(S) independent data streamsto achieve greater overall throughput.

In a multiple-access MIMO system based on SDMA, an access point cancommunicate with one or more user terminals at any given moment. If theaccess point communicates with a single user terminal, then the N_(T)transmit antennas are associated with one transmitting entity (eitherthe access point or the user terminal), and the N_(R) receive antennasare associated with one receiving entity (either the user terminal orthe access point). The access point can also communicate with multipleuser terminals simultaneously via SDMA. For SDMA, the access pointutilizes multiple antennas for data transmission and reception, and eachof the user terminals typically utilizes less than the number of accesspoint antennas for data transmission and reception. When SDMA istransmitted from an access point, N_(S)≦min{N_(T), sum(N_(R))}, wheresum(N_(R)) represents the summation of all user terminal receiveantennas. When SDMA is transmitted to an access point,N_(S)≦min{sum(N_(T)), N_(R)}, where sum(N_(T)) represents the summationof all user terminal transmit antennas.

SUMMARY

Certain embodiments of the present disclosure provide a method forencoding information in a preamble of an orthogonal frequency-divisionmultiplexed (OFDM) wireless communications frame. The method generallyincludes determining a number B of bits, from a plurality of bits of theframe preamble used to specify one or more properties of a transmission,and encoding the information using the B bits, wherein a duration S ofthe transmission measured in OFDM symbols is the same regardless of thevalues of the B bits used to encode the information. For someembodiments, the one or more properties of the transmission may be alength L of the transmission.

Certain embodiments of the present disclosure provide a computer-programproduct for encoding information in a preamble of an OFDM wirelesscommunications frame. The computer-program product typically includes acomputer-readable medium having instructions stored thereon, theinstructions being executable by one or more processors. Theinstructions generally include instructions for determining a number Bof bits, from a plurality of bits of the frame preamble used to specifyone or more properties of a transmission, and instructions for encodingthe information using the B bits, wherein a duration S of thetransmission measured in OFDM symbols is the same regardless of thevalues of the B bits used to encode the information.

Certain embodiments of the present disclosure provide an apparatus forencoding information in a preamble of an OFDM wireless communicationsframe. The apparatus generally includes means for determining a number Bof bits, from a plurality of bits of the frame preamble used to specifyone or more properties of a transmission, and means for encoding theinformation using the B bits, wherein a duration S of the transmissionmeasured in OFDM symbols is the same regardless of the values of the Bbits used to encode the information.

Certain embodiments of the present disclosure provide an access point(AP) for encoding information in a preamble of an OFDM wirelesscommunications frame. The AP generally includes logic for determining anumber B of bits, from a plurality of bits of the frame preamble used tospecify one or more properties of a transmission, and logic for encodingthe information using the B bits, wherein a duration S of thetransmission measured in OFDM symbols is the same regardless of thevalues of the B bits used to encode the information.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to embodiments, someof which are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalembodiments of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective embodiments.

FIG. 1 illustrates a spatial division multiple access (SDMA)multiple-input multiple-output (MIMO) wireless system, in accordancewith certain embodiments of the present disclosure.

FIG. 2 illustrates a block diagram of an access point (AP) and two userterminals, in accordance with certain embodiments of the presentdisclosure.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice, in accordance with certain embodiments of the presentdisclosure.

FIG. 4 illustrates the format of an example legacy IEEE 802.11n signalfield (High Throughput Signal, or HT-SIG), in accordance with certainembodiments of the present disclosure.

FIG. 5 illustrates example operations for encoding information in bitsof a frame preamble, in accordance with certain embodiments of thepresent disclosure.

FIG. 5A is a block diagram of means corresponding to the exampleoperations of FIG. 5 for encoding information in bits of a framepreamble, in accordance with certain embodiments of the presentdisclosure.

FIGS. 6A and 6B illustrate examples for embedding information in theHT-SIG field, in accordance with certain embodiments of the presentdisclosure.

DETAILED DESCRIPTION

Certain embodiments of the present disclosure provide techniques andapparatus for embedding one or more bits of 802.11 Very High Throughput(VHT) information in existing IEEE 802.11 preamble fields. As will bedescribed herein, because different combinations of modulationtechniques, coding schemes, and transmission lengths result in the sametransmit time (e.g., in terms of symbol length), a clever choice ofmodulation, coding, and length may allow some extra information to beembedded in a legacy field for use by VHT stations. In this manner, thetotal VHT preamble transmission time may potentially be reduced, therebyincreasing the efficiency of the physical layer (PHY). Moreover, theembedded bits may most likely be invisible to legacy stations, since thetransmission time that such stations compute will be independent ofthese bits by design.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments. Also as used herein, the term“legacy stations” generally refers to wireless network nodes thatsupport 802.11n or earlier versions of the IEEE 802.11 standard.

The multi-antenna transmission techniques described herein may be usedin combination with various wireless technologies such as Code DivisionMultiple Access (CDMA), Orthogonal Frequency Division Multiplexing(OFDM), Time Division Multiple Access (TDMA), and so on. Multiple userterminals can concurrently transmit/receive data via different (1)orthogonal code channels for CDMA, (2) time slots for TDMA, or (3)subbands for OFDM. A CDMA system may implement IS-2000, IS-95, IS-856,Wideband-CDMA (W-CDMA), or some other standards. An OFDM system mayimplement IEEE 802.11 or some other standards. A TDMA system mayimplement GSM or some other standards. These various standards are knownin the art.

An Example MIMO System

FIG. 1 shows a multiple-access MIMO system 100 with access points anduser terminals. For simplicity, only one access point 110 is shown inFIG. 1. An access point (AP) is generally a fixed station thatcommunicates with the user terminals and may also be referred to as abase station or some other terminology. A user terminal (UT) may befixed or mobile and may also be referred to as a mobile station (MS), awireless device, or some other terminology. Access point 110 maycommunicate with one or more user terminals 120 at any given moment onthe downlink and uplink. The downlink (i.e., forward link) is thecommunication link from the access point to the user terminals, and theuplink (i.e., reverse link) is the communication link from the userterminals to the access point. A user terminal may also communicatepeer-to-peer with another user terminal. A system controller 130 couplesto and provides coordination and control for the access points.

While portions of the following disclosure will describe user terminals120 capable of communicating via SDMA, for certain embodiments, the userterminals 120 may also include some user terminals that do not supportSDMA. Thus, for such embodiments, an AP 110 may be configured tocommunicate with both SDMA and non-SDMA user terminals. This approachmay conveniently allow older versions of user terminals (“legacy”stations) to remain deployed in an enterprise, extending their usefullifetime, while allowing newer SDMA user terminals to be introduced asdeemed appropriate.

System 100 employs multiple transmit and multiple receive antennas fordata transmission on the downlink and uplink. Access point 110 isequipped with a number N_(ap) of antennas and represents themultiple-input (MI) for downlink transmissions and the multiple-output(MO) for uplink transmissions. A set N_(u) of selected user terminals120 collectively represents the multiple-output for downlinktransmissions and the multiple-input for uplink transmissions. For pureSDMA, it is desired to have N_(ap)≧N_(u)≧1 if the data symbol streamsfor the N_(u) user terminals are not multiplexed in code, frequency, ortime by some means. N_(u) may be greater than N_(ap) if the data symbolstreams can be multiplexed using different code channels with CDMA,disjoint sets of sub-bands with OFDMA, and so on. Each selected userterminal transmits user-specific data to and/or receives user-specificdata from the access point. In general, each selected user terminal maybe equipped with one or multiple antennas (i.e., N_(ut)≧1). The N_(u)selected user terminals can have the same or different number ofantennas.

MIMO system 100 may be a time division duplex (TDD) system or afrequency division duplex (FDD) system. For a TDD system, the downlinkand uplink share the same frequency band. For an FDD system, thedownlink and uplink use different frequency bands. MIMO system 100 mayalso utilize a single carrier or multiple carriers for transmission.Each user terminal may be equipped with a single antenna (e.g., in orderto keep costs down) or multiple antennas (e.g., where the additionalcost can be supported).

FIG. 2 shows a block diagram of access point 110 and two user terminals120 m and 120 x in MIMO system 100. Access point 110 is equipped withN_(ap) antennas 224 a through 224 ap. User terminal 120 m is equippedwith N_(ut,m) antennas 252 ma through 252 mu, and user terminal 120 x isequipped with N_(ut,x) antennas 252 xa through 252 xu. Access point 110is a transmitting entity for the downlink and a receiving entity for theuplink. Each user terminal 120 is a transmitting entity for the uplinkand a receiving entity for the downlink. As used herein, a “transmittingentity” is an independently operated apparatus or device capable oftransmitting data via a wireless channel, and a “receiving entity” is anindependently operated apparatus or device capable of receiving data viaa wireless channel. In the following description, the subscript “dn”denotes the downlink, the subscript “up” denotes the uplink, N_(up) userterminals are selected for simultaneous transmission on the uplink,N_(dn) user terminals are selected for simultaneous transmission on thedownlink, N_(up) may or may not be equal to N_(dn), and N_(up) andN_(dn) may be static values or can change for each scheduling interval.The beam-steering or some other spatial processing technique may be usedat the access point and user terminal.

On the uplink, at each user terminal 120 selected for uplinktransmission, a TX data processor 288 receives traffic data from a datasource 286 and control data from a controller 280. TX data processor 288processes (e.g., encodes, interleaves, and modulates) the traffic data{d_(up,m)} for the user terminal based on the coding and modulationschemes associated with the rate selected for the user terminal andprovides a data symbol stream {s_(up,m)}. A TX spatial processor 290performs spatial processing on the data symbol stream {s_(up,m)} andprovides N_(ut,m) transmit symbol streams for the N_(ut,m) antennas.Each transmitter unit (TMTR) 254 receives and processes (e.g., convertsto analog, amplifies, filters, and frequency upconverts) a respectivetransmit symbol stream to generate an uplink signal. N_(ut,m)transmitter units 254 provide N_(ut,m) uplink signals for transmissionfrom N_(ut,m) antennas 252 to the access point 110.

A number N_(up) of user terminals may be scheduled for simultaneoustransmission on the uplink. Each of these user terminals performsspatial processing on its data symbol stream and transmits its set oftransmit symbol streams on the uplink to the access point.

At access point 110, N_(ap) antennas 224 a through 224 ap receive theuplink signals from all N_(up) user terminals transmitting on theuplink. Each antenna 224 provides a received signal to a respectivereceiver unit (RCVR) 222. Each receiver unit 222 performs processingcomplementary to that performed by transmitter unit 254 and provides areceived symbol stream. An RX spatial processor 240 performs receiverspatial processing on the N_(ap) received symbol streams from N_(ap)receiver units 222 and provides N_(up) recovered uplink data symbolstreams. The receiver spatial processing is performed in accordance withthe channel correlation matrix inversion (CCMI), minimum mean squareerror (MMSE), successive interference cancellation (SIC), or some othertechnique. Each recovered uplink data symbol stream {s_(up,m)} is anestimate of a data symbol stream {s_(up,m)} transmitted by a respectiveuser terminal. An RX data processor 242 processes (e.g., demodulates,deinterleaves, and decodes) each recovered uplink data symbol stream{s_(up,m)} in accordance with the rate used for that stream to obtaindecoded data. The decoded data for each user terminal may be provided toa data sink 244 for storage and/or a controller 230 for furtherprocessing.

On the downlink, at access point 110, a TX data processor 210 receivestraffic data from a data source 208 for N_(dn) user terminals scheduledfor downlink transmission, control data from a controller 230, andpossibly other data from a scheduler 234. The various types of data maybe sent on different transport channels. TX data processor 210 processes(e.g., encodes, interleaves, and modulates) the traffic data for eachuser terminal based on the rate selected for that user terminal. TX dataprocessor 210 provides N_(dn) downlink data symbol streams for theN_(dn) user terminals. A TX spatial processor 220 performs spatialprocessing on the N_(dn) downlink data symbol streams, and providesN_(ap) transmit symbol streams for the N_(ap) antennas. Each transmitterunit (TMTR) 222 receives and processes a respective transmit symbolstream to generate a downlink signal. N_(ap) transmitter units 222provide N_(ap) downlink signals for transmission from N_(ap) antennas224 to the user terminals.

At each user terminal 120, N_(ut,m) antennas 252 receive the N_(ap)downlink signals from access point 110. Each receiver unit (RCVR) 254processes a received signal from an associated antenna 252 and providesa received symbol stream. An RX spatial processor 260 performs receiverspatial processing on N_(ut,m) received symbol streams from N_(ut,m)receiver units 254 and provides a recovered downlink data symbol stream{s_(dn,m)} for the user terminal. The receiver spatial processing isperformed in accordance with the CCMI, MMSE, or some other technique. AnRX data processor 270 processes (e.g., demodulates, deinterleaves, anddecodes) the recovered downlink data symbol stream to obtain decodeddata for the user terminal.

At each user terminal 120, a channel estimator 278 estimates thedownlink channel response and provides downlink channel estimates, whichmay include channel gain estimates, SNR estimates, and so on. Similarly,a channel estimator 228 estimates the uplink channel response andprovides uplink channel estimates. Controller 280 for each user terminaltypically derives the spatial filter matrix for the user terminal basedon the downlink channel response matrix H_(dn,m) for that user terminal.Controller 230 derives the spatial filter matrix for the access pointbased on the effective uplink channel response matrix H_(up,eff).Controller 280 for each user terminal may send feedback information(e.g., the downlink and/or uplink steering vectors, SNR estimates, andso on) to the access point. Controllers 230 and 280 also control theoperation of various processing units at access point 110 and userterminal 120, respectively.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice 302 that may be employed within the system 100. The wirelessdevice 302 is an example of a device that may be configured to implementthe various methods described herein. The wireless device 302 may be anaccess point 110 or a user terminal 120.

The wireless device 302 may include a processor 304 which controlsoperation of the wireless device 302. The processor 304 may also bereferred to as a central processing unit (CPU). Memory 306, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 304. A portion of thememory 306 may also include non-volatile random access memory (NVRAM).The processor 304 typically performs logical and arithmetic operationsbased on program instructions stored within the memory 306. Theinstructions in the memory 306 may be executable to implement themethods described herein.

The wireless device 302 may also include a housing 308 that may includea transmitter 310 and a receiver 312 to allow transmission and receptionof data between the wireless device 302 and a remote location. Thetransmitter 310 and receiver 312 may be combined into a transceiver 314.A plurality of transmit antennas 316 may be attached to the housing 308and electrically coupled to the transceiver 314. The wireless device 302may also include (not shown) multiple transmitters, multiple receivers,and multiple transceivers.

The wireless device 302 may also include a signal detector 318 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 314. The signal detector 318 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 302 may alsoinclude a digital signal processor (DSP) 320 for use in processingsignals.

The various components of the wireless device 302 may be coupledtogether by a bus system 322, which may include a power bus, a controlsignal bus, and a status signal bus in addition to a data bus.

Embedding Information in an 802.11n Signal Field

In IEEE 802.11 WLAN (Wireless Local Area Network) systems, transmittedframes have a preamble that allows stations to synchronize and obtaininformation, such as the length and coding rate, about the data packetthat follows. The design of the next generation 802.11 Very HighThroughput (VHT) system may require a new preamble structure. A typicalscheme for signaling VHT preamble information may include allVHT-related information bits in a VHT signal field. Such a VHT signalfield may generally be coded at a low data rate to ensure all stationscan decode it.

As a result, however, the VHT signal field may be relatively inefficientin terms of data rate. For example, in the 802.11n standard, the signalfield may require 8 μs to carry 34 bits of information. Therefore,although it is simple to put all VHT-related bits in the VHT signalfield, this approach may cause long preamble transmission times due tothe low rate. Accordingly, if the number of VHT-related bits in the VHTsignal field could be somehow reduced, the length of the preamble may bedecreased, and the physical layer (PHY) efficiency may be increased.

FIG. 4 is a diagram illustrating the format of an example legacy 802.11nsignal field known as a High Throughput Signal (HT-SIG) field 400,although any legacy field suitable for embedding VHT bits may be used.FIG. 4 illustrates the format of a first 24-bit portion HT-SIG₁ 410 ofthe 48-bit HT-SIG field 400 and the format of a second 24-bit portionHT-SIG₂ 450. The first portion HT-SIG₁ 410 includes a 7-bit Modulationand Coding Scheme (MCS) field 420 for conveying the index to themodulation technique and the coding rate used by the access point 110. A1-bit bandwidth (BW 20/40) field 430 follows the MCS field 420 and maybe used to indicate whether 20 MHz or 40 MHz is used. HT-SIG₁ 410 alsocomprises a 16-bit HT Length field 440 for conveying information aboutthe number of bytes of data in the PSDU (PLCP service data unit, wherePLCP stands for physical layer convergence procedure). The bits inHT-SIG₁ 410 are arranged from least significant bit (LSB) to mostsignificant bit (MSB) As will be described herein, for certainembodiments, some number of LSBs of the HT Length field 440 may be usedto encode VHT information.

FIG. 5 illustrates example operations 500 for encoding information inbits of a frame preamble, according to one embodiment of the disclosure.The operations 500 begin at 510, where a number B of bits are determinedfrom a plurality of the bits of the frame preamble used to specify oneor more properties of a transmission (e.g., length). At 520, the B bits(determined at 510) are used to encode the information, wherein aduration S of the transmission measured in orthogonal frequency divisionmultiplexed (OFDM) symbols is the same regardless of the values of the Bbits used to encode the information. In this manner, B VHT-relatedinformation bits may be embedded in the frame preamble, therebyshortening the number of VHT-related information bits (by B bits) thatmay be included in a VHT signal field and, in turn, shortening the totalpreamble transmission time. Determining a number B of bits and aduration of S symbols is described in greater detail below.

In an effort to embed information bits in an existing preamble field,the relationship between the MCS/length combination and the transmittime may be determined. Assume that R is the data rate in Mbps (megabitsper second), which may be set by the MCS field 420 of HT-SIG 400. Alsoassume that L is the transmission length in bytes, and S is thetransmission duration in OFDM symbols. Assume further that 4 μs persymbol is used when calculating R, resulting in the following formula:

$S = \left\lceil \frac{2L}{R} \right\rceil$Rounding up in the above equation is used since the number of symbols Smust be a whole number (i.e., without a fractional part). Therealization that different transmission lengths L can yield the sametransmission duration S for a given data rate R according to the aboveequation is what allows for a number B of bits to be embedded in the HTLength field 440 of HT-SIG 400. For a given S, the range of the length Lis given by the following formula:

$\frac{R\left( {S - 1} \right)}{2} < L \leq \frac{RS}{2}$

According to embodiments of the present disclosure, there is a desire toembed information in the least significant B bits of the HT Length field440 without affecting the transmission duration S. In such a situation,an integer k is determined such that the length expression L₀=2^(B)k(where L₀<2¹⁶ for the 16-bit HT Length field 440) satisfies thefollowing condition:

$\left. {{2^{B}k} > {{\frac{R\left( {S - 1} \right)}{2}\mspace{14mu}{and}\mspace{14mu} 2^{B}k} + 2^{B} - 1} \leq \frac{RS}{2}}\Rightarrow{\frac{R\left( {S - 1} \right)}{2^{B + 1}} < k \leq {\frac{{RS} + 2}{2^{B - 1}} - 1}} \right.$Note that an integer solution k will always exist under the followingcondition:

$\left. {{\frac{{RS} + 2}{2^{B - 1}} - 1 - \frac{R\left( {S - 1} \right)}{2^{B + 1}}} \geq 1}\Rightarrow{R \geq {2^{B + 2} - 2}} \right.$Thus, one possible solution for the length expression is the following:

$L_{0} = {2^{B}\left\lfloor {\frac{{RS} + 2}{2^{B + 1}} - 1} \right\rfloor}$

FIG. 6A illustrates a first example of determining a transmissionduration S, according to certain embodiments of the disclosure. In thisexample, suppose a desire to embed B=5 bits of information, such asVHT-related information bits. Assume also that the index of theModulation and Coding Scheme field 420 of HT-SIG 400 is 15 (MCS 15) suchthat R=130 Mbps in 20 MHz. Note that R≧2^(B+2)−2=126. For a transmissionduration of S symbols, the result is:

$L_{0} = {32\left\lfloor {\frac{{130S} + 2}{64} - 1} \right\rfloor}$Thus, in this example, the 5 LSBs of L₀ can be set to any value requiredto carry information, and the resulting transmission duration S willalways be constant per the following formula:

$S = \left\lceil \frac{2L}{R} \right\rceil$In other words, the 5 LSBs (b₀ to b₄) 600 of the 16-bit HT Length field440 may contain VHT-related information. In this example, a transmissionduration S=1008 symbols is the maximum allowed to keep L₀ within 16bits. This enables a transmission opportunity (TXOP) of up to 4 ms.

FIG. 6B illustrates a second example of determining a transmissionduration S, according to certain embodiments of the disclosure. In thisexample, suppose a desire to embed B=6 bits of information. Assume alsothat the index of the Modulation and Coding Scheme field 420 of HT-SIG400 is 31 (MCS 31) is selected such that R=260 Mbps in 20 MHz. Note thatR≧2^(B+2)−2=254. For a transmission duration of S symbols, the resultis:

$L_{0} = {64\left\lfloor {\frac{{260S} + 2}{128} - 1} \right\rfloor}$Thus, in this example, the 6 LSBs of L₀ can be set to any value requiredto carry information, and the resulting transmission duration S willalways be constant. In other words, the 6 LSBs (b₀ to b₅) 650 of the16-bit HT Length field 440 may contain VHT-related information. In thisexample, a transmission duration S=504 symbols is the maximum allowed tokeep L₀ within 16 bits. This enables a TXOP of up to 2 ms.

To note, there may be one broadcast HT-SIG field 400 intended forreception by many stations (STAs), transmitted, for example, via an SDMAdownlink. Therefore, the VHT-related information selected for bitsembedded in the HT-SIG field 400 may most likely carry generalinformation about the network. VHT STAs in a network would know aboutthe embedded bits according to embodiments of the present disclosure andwould be able to interpret them, whereas legacy STAs may most likelyoverlook these embedded bits and only interpret such bits as conveyingpart of the length of the PSDU.

The various operations of methods described above may be performed byvarious hardware and/or software component(s) and/or module(s)corresponding to means-plus-function blocks illustrated in the figures.Generally, where there are methods illustrated in figures havingcorresponding counterpart means-plus-function figures, the operationblocks correspond to means-plus-function blocks with similar numbering.For example, blocks 510-520 illustrated in FIG. 5 correspond tomeans-plus-function blocks 510A-520A illustrated in FIG. 5A.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining, and thelike. Also, “determining” may include receiving (e.g., receivinginformation), accessing (e.g., accessing data in a memory), and thelike. Also, “determining” may include resolving, selecting, choosing,establishing, and the like.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, and the like that may be referencedthroughout the above description may be represented by voltages,currents, electromagnetic waves, magnetic fields or particles, opticalfields or particles, or any combination thereof.

The various illustrative logical blocks, modules, and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware components,or any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thepresent disclosure may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in any form of storage medium that is knownin the art. Some examples of storage media that may be used includerandom access memory (RAM), read only memory (ROM), flash memory, EPROMmemory, EEPROM memory, registers, a hard disk, a removable disk, aCD-ROM and so forth. A software module may comprise a singleinstruction, or many instructions, and may be distributed over severaldifferent code segments, among different programs, and across multiplestorage media. A storage medium may be coupled to a processor such thatthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware, or any combination thereof. If implemented in software, thefunctions may be stored as one or more instructions on acomputer-readable medium. A storage media may be any available mediathat can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition oftransmission medium.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

1. A method for encoding information in a preamble of an orthogonalfrequency-division multiplexed (OFDM) wireless communications frame,comprising: determining a number B of bits, from a plurality of bits ofthe frame preamble used to specify one or more properties of atransmission; and encoding the information using the B bits, wherein aduration S of the transmission measured in OFDM symbols is the sameregardless of the values of the B bits used to encode the information,wherein the one or more properties of the transmission comprise a lengthL of the transmission, and wherein a data rate R is measured in megabitsper second (Mbps) and the length L in bytes may range between R(S−1)/2<LRS/2 for the duration S assuming 4 μs per symbol for the data rate R. 2.The method of claim 1, wherein determining the number B of bitscomprises determining a data rate R and a symbol period.
 3. The methodof claim 1, wherein determining the number B of bits comprises using alookup table according to a data rate R and the duration S of thetransmission.
 4. The method of claim 1, wherein the plurality of bitsused to specify the length L are in a High Throughput Signal (HT-SIG)field of the frame preamble.
 5. The method of claim 4, wherein the Bbits are least significant bits (LSBs) of an HT Length field of theHT-SIG field.
 6. The method of claim 1, wherein the data rate R isspecified in a Modulation and Coding Scheme (MCS) field of a HighThroughput Signal (HT-SIG) field of the frame preamble.
 7. The method ofclaim 1, wherein determining the number B of bits comprises selectingthe data rate R such that R(S−1)/2^(B+1)<k≦RS+2/2^(B+1)−1 has an integersolution k.
 8. The method of claim 7, wherein determining the number Bof bits comprises determining a length L₀ such that L₀=2^(B)k, where kis an integer such that$\frac{R\left( {S - 1} \right)}{2^{B + 1}} < k \leq {\frac{{RS} + 2}{2^{B + 1}} - 1.}$9. The method of claim 1, wherein the data rate R=130 Mbps, the number Bof bits is 5, and the length L is less than 2¹⁶.
 10. The method of claim1, wherein the data rate R=260 Mbps, the number B of bits is 6, and thelength L is less than 2¹⁶.
 11. A computer-program product for encodinginformation in a preamble of an orthogonal frequency-divisionmultiplexed (OFDM) wireless communications frame, comprising anon-transitory computer-readable medium having instructions storedthereon, the instructions being executable by one or more processors andthe instructions comprising: instructions for determining a number B ofbits, from a plurality of bits of the frame preamble used to specify oneor more properties of a transmission; and instructions for encoding theinformation using the B bits, wherein a duration S of the transmissionmeasured in OFDM symbols is the same regardless of the values of the Bbits used to encode the information, wherein the one or more propertiesof the transmission comprise a length L of the transmission, and whereina data rate R is measured in megabits per second (Mbps) and the length Lin bytes may range between$\frac{R\left( {S - 1} \right)}{2} < L \leq \frac{RS}{2}$ for theduration S assuming 4 μs per symbol for the data rate R.
 12. Thecomputer-program product of claim 11, wherein the instructions fordetermining the number B of bits comprise instructions for determining adata rate R and a symbol period.
 13. The computer-program product ofclaim 11, wherein the instructions for determining the number B of bitscomprise instructions for using a lookup table according to a data rateR and the duration S of the transmission.
 14. The computer-programproduct of claim 11, wherein the plurality of bits used to specify thelength L are in a High Throughput Signal (HT-SIG) field of the framepreamble.
 15. The computer-program product of claim 14, wherein the Bbits are least significant bits (LSBs) of an HT Length field of theHT-SIG field.
 16. The computer-program product of claim 11, wherein thedata rate R is specified in a Modulation and Coding Scheme (MCS) fieldof a High Throughput Signal (HT-SIG) field of the frame preamble. 17.The computer-program product of claim 11, wherein the instructions fordetermining the number B of bits comprise instructions for selecting thedata rate R such that$\frac{R\left( {S - 1} \right)}{2^{B + 1}} < k \leq {\frac{{RS} + 2}{2^{B + 1}} - 1}$has an integer solution k.
 18. The computer-program product of claim 17,wherein the instructions for determining the number B of bits compriseinstructions for determining a length L₀ such that L₀=2^(B)k, where k isan integer such that$\frac{R\left( {S - 1} \right)}{2^{B + 1}} < k \leq {\frac{{RS} + 2}{2^{B + 1}} - 1.}$19. An apparatus for encoding information in a preamble of an orthogonalfrequency-division multiplexed (OFDM) wireless communications frame,comprising: means for determining a number B of bits, from a pluralityof bits of the frame preamble used to specify one or more properties ofa transmission; and means for encoding the information using the B bits,wherein a duration S of the transmission measured in OFDM symbols is thesame regardless of the values of the B bits used to encode theinformation, wherein the one or more properties of the transmissioncomprise a length L of the transmission, and wherein a data rate R ismeasured in megabits per second (Mbps) and the length L in bytes mayrange between $\frac{R\left( {S - 1} \right)}{2} < L \leq \frac{RS}{2}$for the duration S assuming 4 μs per symbol for the data rate R.
 20. Theapparatus of claim 19, wherein the means for determining the number B ofbits comprise means for determining a data rate R and a symbol period.21. The apparatus of claim 19, wherein the means for determining thenumber B of bits comprises means for using a lookup table according to adata rate R and the duration S of the transmission.
 22. The apparatus ofclaim 19, wherein the plurality of bits used to specify the length L arein a High Throughput Signal (HT-SIG) field of the frame preamble. 23.The apparatus of claim 22, wherein the B bits are least significant bits(LSBs) of an HT Length field of the HT-SIG field.
 24. The apparatus ofclaim 19, wherein the data rate R is specified in a Modulation andCoding Scheme (MCS) field of a High Throughput Signal (HT-SIG) field ofthe frame preamble.
 25. The apparatus of claim 19, wherein the means fordetermining the number B of bits comprise means for selecting the datarate R such that$\frac{R\left( {S - 1} \right)}{2^{B + 1}} < k \leq {\frac{{RS} + 2}{2^{B + 1}} - 1}$has an integer solution k.
 26. The apparatus of claim 25, wherein themeans for determining the number B of bits comprise means fordetermining a length L₀ such that L₀=2^(B)k, where k is an integer suchthat$\frac{R\left( {S - 1} \right)}{2^{B + 1}} < k \leq {\frac{{RS} + 2}{2^{B + 1}} - 1.}$27. An access point (AP) for encoding information in a preamble of anorthogonal frequency-division multiplexed (OFDM) wireless communicationsframe, comprising: logic for determining a number B of bits, from aplurality of bits of the frame preamble used to specify one or moreproperties of a transmission; and logic for encoding the informationusing the B bits, wherein a duration S of the transmission measured inOFDM symbols is the same regardless of the values of the B bits used toencode the information, wherein the one or more properties of thetransmission comprise a length L of the transmission, and wherein a datarate R is measured in megabits per second (Mbps) and the length L inbytes may range between$\frac{R\left( {S - 1} \right)}{2} < L \leq \frac{RS}{2}$ for theduration S assuming 4 μs per symbol for the data rate R.
 28. The accesspoint of claim 27, wherein the logic for determining the number B ofbits is configured to determine a data rate R and a symbol period. 29.The access point of claim 27, wherein the logic for determining thenumber B of bits is configured to use a lookup table according to a datarate R and the duration S of the transmission.
 30. The access point ofclaim 27, wherein the plurality of bits used to specify the length L arein a High Throughput Signal (HT-SIG) field of the frame preamble. 31.The access point of claim 30, wherein the B bits are least significantbits (LSBs) of an HT Length field of the HT-SIG field.
 32. The accesspoint of claim 27, wherein the data rate R is specified in a Modulationand Coding Scheme (MCS) field of a High Throughput Signal (HT-SIG) fieldof the frame preamble.
 33. The access point of claim 27, wherein thelogic for determining the number B of bits is configured to select thedata rate R such that$\frac{R\left( {S - 1} \right)}{2^{B + 1}} < k \leq {\frac{{RS} + 2}{2^{B + 1}} - 1}$has an integer solution k.
 34. The access point of claim 33, wherein thelogic for determining the number B of bits is configured to determine alength L₀ such that L₀=2^(B)k, where k is an integer such that$\frac{R\left( {S - 1} \right)}{2^{B + 1}} < k \leq {\frac{{RS} + 2}{2^{B + 1}} - 1.}$